The present invention relates to line powered data communication apparatus (DCA) in general, and more particularly, to a line powered DCA with dual programmed digital signal processors (DSP's), one being interfaceable with data terminal equipment and the other for governing the operation of modem circuitry which is interfaceable to a telephone line of a telephone network, the dual programmed DSP's interacting with each other over an electrically isolated interface.
Line powered DCA's, which may include modems, for example, generally comprise one side or portion which is interfaceable with data terminal equipment (DTE) and another side or portion interfaceable with the telephone network, the two sides being electrically isolated from one another. The DCA circuitry of the one side deriving its power from the DTE interface and the DCA circuitry of the other side deriving its power from the telephone network connection. Early versions of the line powered modem lacked the capability of performing automatically functions such as dial, answer or configuration, for example. Examples of these early models are found in the U.S. Pat. No. 4,578,533 issued Mar. 25, 1986; U.S. Pat. No. 4,417,099 issued Nov. 22, 1983; U.S. Pat. No. 4,415,774 issued Nov. 15, 1983; U.S. Pat. No. 4,395,590 issued Jul. 26, 1983; and U.S. Pat. No. 4,373,117 issued Feb. 8, 1983, all assigned to the same assignee as the instant application. Another patent reference is the U.S. Pat. No. 4,592,069 issued May 27, 1986. In addition, these early versions included a substantial number of electrically isolating devices which were relatively expensive compared with the cost of the other circuit elements.
To eliminate some of the electrically isolating devices and provide some automatic features, the more recent versions of the line powered modems included a single microcontroller disposed on the DTE side for interfacing with the DTE and electrically isolated from the telephone line side thereof. Examples of these more contemporary units are found in the U.S. Pat. No. 4,961,220 issued Oct. 2, 1990 (filed Dec. 21, 1988); and U.S. Pat. No. 4,907,254 issued Mar. 6, 1990. A further example of a line powered modem product employing a single microcontroller is the Stowaway 2400 manufactured by Vocal Technologies Ltd. which was announced in an article in PC Week on Nov. 13, 1989.
While these more recent models appear to alleviate the drawbacks of the earlier versions by providing some automatic features and reducing the number of electrically isolating devices, there remains room for further improvement. More specifically, further flexibility for adding additional features is still desired on the telephone line side which is presently limited to either hard-wired circuitry or a custom integrated circuit. In addition, a further reduction in the number of electrically isolating devices is desired especially because of their relative high costs. The present invention intends to provide for the additional flexibility for adding more features and for a reduction in the number of isolating devices.